Syntheses, crystal structures, and magnetic properties of two novel Ni(mnt)2-based molecular magnetic materials containing substituted triphenylphosphinium

Two novel molecular magnetic materials, [RBzTPP][Ni(mnt)₂] (mnt²⁻ = maleonitriledithiolate, [RBzTPP]⁺ = 4-R-benzyltriphenylphosphinium; R = CN (1), Cl (2)) were synthesized and characterized by X-ray diffraction, IR spectroscopy, and magnetic susceptibility measurements. In crystal of 1, the [Ni(mnt)₂]⁻ anions form a dimer via Ni?S and π?π stacking interactions between Ni(mnt)₂ planes, and the C-H?Ni and C-H?N H-bonding interactions are found between the [Ni(mnt)₂]⁻ anions and the neighboring [CNBzTPP]⁺ cations. The anions and cations of 2 stack into well-segregated columns in the solid state; and the Ni(III) ions form a 1D alternating chain in a Ni(mnt)₂ column through intermolecular Ni?S, or π?π interactions with the Ni?Ni distances of 3.900, 4.198, and 4.165 Å. Magnetic susceptibility measurements for these complexes in the temperature range 1.8-300 K show that the overall magnetic behavior for 1 and 2 indicates the presence of antiferromagnetic interaction, but 1 exhibits an activated magnetic behavior in the high-temperature (HT) region together with a Curie tail in the low-temperature (LT) region.     

Two new ion-pair complexes containing derivatives of substituted benzyl isoquinolinium and bis(maleonitriledithiolato)nickelate monoanion: 3D crystal structures, magnetic properties and theoretical analyses

Syntheses, structural characterizations, magnetic behaviors and theoretical analyses of two new ion-pair complexes, [IFBzIQl][Ni(mnt)₂](1) and [IClBzIQl]₂[Ni(mnt)₂]₂ · MeCN(2) [IFBzIQl][Ni(mnt)₂] ([IFBzIQl]⁺ = 1-(2′-fluoro-4′-iodobenzyl)isoquinolinium, [IClBzIQl]⁺ = 1-(2′-chloro-4′-iodobenzyl)isoquinolinium, mnt²⁻ = maleonitriledithiolate), have been investigated. In crystal of 1, the [Ni(mnt)₂]⁻ anions and the [IFBzIQl]⁺ cations stack into an alternating column through π?π stacking interactions. The anions of both 1 and 2 form a dimer via π?π stacking and S?S short interactions between the [Ni(mnt)₂]⁻ anions. The overlapping mode of two neighboring [Ni(mnt)₂]⁻ anions in the dimer is the Ni-ring fashion with a Ni?Ni distance of 4.076 Å for 1, and ring-ring fashion with the Ni?Ni and S?S distances being 4.395 and 3.593 Å for 2. Some weak interactions such as π?π, C?N, C-H?F or C-H?N in 1 and 2 play a crucial role in stacking and stabilizing the crystal lattice, and give a 3D network structure and exchange pathways of the magnetic interaction for 1 and 2. Magnetic susceptibility measurements for 1 and 2 in the temperature range 1.8-300 K show that the overall magnetic behavior indicates the presence of antiferromagnetic interaction, while 2 exhibits an activated magnetic behavior in the high-temperature region (HT) together with a Curie tail in the low-temperature region (LT).     

2D crystal structure, magnetic behavior and theoretic analysis of two new molecular solids based on Ni(maleonitriledithiolate)2 monoanion with substituted 2-aminopyridinium

Two new molecular solids, [BzPyNH₂][Ni(mnt)₂](1) and [2-NpCH₂PyNH₂][Ni(mnt)₂](2) (mnt²⁻ = maleonitriledithiolate, [BzPyNH₂]⁺ = 1-benzyl-2-aminopyridinium and [2-NpCH₂PyNH₂]⁺ = 1-(2′-naphthylmethylene)-2-aminopyridinium) have been characterized structurally and magnetically. The Ni(Ш) ions of 1 and 2 form a 1D magnetic chain within a [Ni(mnt)₂]⁻ column through Ni?N or π?π interactions. Some weak interactions observed in 1 and 2 give further rise to a 2D structure. The overlapping fashions of the [Ni(mnt)₂]⁻ anions are different when the 2-aminopyridine ring was fixed and the phenyl ring changed into the naphthyl ring of the cation. Magnetic susceptibility measurements in the temperature range 2-300 K show that 1 is weak antiferromagnetic coupling, while 2 exhibits a novel and interesting spin-gap transition around 140 K with Δ/k_b = 381.4 K.     

3D network structure and spin gap behavior in two new molecular magnets based on bis(maleonitriledithiolato)nickelate monoanion

Two new molecular magnets, based on [Ni(mnt)₂]⁻ monoanion, [DiBrBzPy][Ni(mnt)₂] (1) and [DiBrBzIQl][Ni(mnt)₂] (2) ([DiBrBzPy]⁺ = 1-(3′,5′-dibromobenzyl)pyridinium, [DiBrBzIQl]⁺ = 1-(3′,5′-dibromobenzyl)isoquinolinium and mnt²⁻ = maleonitriledithiolate), were prepared and characterized by elemental analyses, IR, ESI-MS spectra, single crystal X-ray diffraction and magnetic measurements. The [Ni(mnt)₂] anions and the cations of 1 and 2 are alternately stacked and form 1D column via π?π stacking interactions between the [Ni(mnt)₂] anions and the neighboring cations. Some weak Ni?N, C?N interactions and CH?Br, CH?N hydrogen bonds between the adjacent columns further generate a 3D network structure. Magnetic susceptibility measurements show that both 1 and 2 exhibit the typical magnetic behavior of a spin gap system with an energy gap of 1151.9 K for 1 and 73.9 K for 2.     

Syntheses, crystal structures, and magnetic properties of Ni(mnt)2-based molecular solids containing substituted isoquinolinium

Two novel ion-pair complexes, [RBzIQl]⁺[Ni(mnt)₂]⁻ (mnt²⁻ = maleonitriledithiolate, [RBzIQl]⁺ = 4-R-benzylisoquinolinium; R = H (1), Cl (2)) have been characterized structurally and magnetically. The anions and [BzIQl]⁺ cations of 1 form 1D column of alternating between cations and anions via π?π stacking interaction between Ni(mnt)₂ plane and isoquinoline ring, and the Ni(mnt)₂ anions between adjacent columns exist C?N, C?N, and N?N interaction. The anions and cations of 2 stack into well-segregated columns in the solid state; and the Ni(III) ions form a 1D zigzag chain in a Ni(mnt)₂ column through intermolecular Ni?S, S?S, Ni?Ni or π?π interactions. The chain is uniform in 2 with the Ni?Ni distances of 3.784 Å. Magnetic susceptibility measurements for these complexes in the temperature range 1.8-300 K show that 1 exhibits antiferromagnetic coupling behavior, and 2 exhibits unusual magnetic phase transitions around 45 K. The overall magnetic behavior for 2 indicates the presence of antiferromagnetic interaction in the high-temperature phase (HT) and spin gap in the low-temperature phase (LT).     

Synthesis, crystal structure and magnetic characterization of two new ion-pair complexes containing bis(maleonitriledithiolate)nickelate anion and substituted benzylpyridinium cation

Two new ion-pair complexes, [FBrBzPyN(CH₃)₂]₂[Ni(mnt)₂] (1) and [FBrBzPyN(CH₃)₂][Ni(mnt)₂] (2) (mnt²⁻ = maleonitriledithiolate, [FBrBzPyN(CH₃)₂]⁺ = [1-(4′-fluoro-2′-bromobenzyl)-4-dimethylaminopyridinium]) have been prepared and characterized by elemental analyses, UV, IR, single crystal X-ray diffraction and magnetic susceptibility. The cations (D) and the anions (A) in 1 stack into a 1D alternating column (i.e., of type ?DDADDADD?) via short S?Br, N?F, C?N interactions, and C-H?Br hydrogen bonds. The cation-cation π?π stacking interactions within the columns give further rise to a 2D network structure. Compound 2 forms a 3D structure in which the Ni(III) ions stack into a uniform 1D zigzag magnetic chain through Ni?S, Ni?Ni, or π?π interactions with a Ni?Ni distance of 4.024 Å. Magnetic susceptibility measurements in the temperature range 2-300 K show that 1 is expected to be diamagnetic, and 2 exhibits an interesting spin-gap transition (Δ/k_b = 460.6 K) around 155 K.     

Use of a cubane-type Mo3CoS4 molecular cluster as paramagnetic unit in the synthesis of hybrid charge-transfer salts

Selective substitution of the chlorine atom coordinated to cobalt in the paramagnetic Mo₃(CoCl)S₄(dmpe)₃Cl₃ (dmpe = 1,2-bis(dimethylphosphanyl) ethane) complex with a S = 1/2 ground state has been achieved by iodine oxidation to afford the also paramagnetic [Mo₃(CoI)S₄(dmpe)₃Cl₃]I ([1]I) salt with a S = 1 ground state in almost quantitative yield. Replacement of chorine by iodine has no significant effect on the structural and electrochemical properties of the Mo₃CoS₄ system. Metathesis of the [1]I salt with the paramagnetic nickel anionic dithiolate [Ni(mnt)₂]⁻ (mnt = maleonitrilodithiolate) affords [1]₂[Ni(mnt)₂]. The stoichiometry evidenced by X-ray analysis reveals that reduction of the [Ni(mnt)₂]⁻ radical to the corresponding diamagnetic closed shell [Ni(mnt)₂]²⁻ dianion, presumably via dismutation, has occurred during the metathesis process. The crystal structure of [1]₂[Ni(mnt)₂] consists of [Ni(mnt)₂]²⁻ dianions sandwiched by two cluster 1⁺ cations which yield {1⁺·[Ni(mnt)₂]²⁻·1⁺} subunits arranged along the crystallographic c axis. Magnetic susceptibility measurements for [1]₂[Ni(mnt)₂] show a χT product of 0.99 emu K/mol largely unchanged in the 10-300 K range. This behavior agrees with the presence of an S = 1 cluster 1⁺ cation while the Ni(mnt)₂ moiety does not contribute to the paramagnetism of the sample.     

Syntheses, structures, and magnetic properties of two new molecular magnets containing Ni(mnt)2 monoanion and substituted 4-dimethylaminopyridinium

Two new molecular magnets, [BzPyN(CH₃)₂][Ni(mnt)₂] (1) and [NO₂BzPyN(CH₃)₂][Ni(mnt)₂] (2)([BzPyN(CH₃)₂]⁺ = 1-benzyl-4-dimethylaminopyridinium, [NO₂BzPyN(CH₃)₂]⁺ = 1-(4′-nitrobenzyl)-4-dimethylaminopyridinium, and mnt²⁻ = maleonitriledithiolate) have been prepared and characterized by elemental analyses, IR, MS spectra, single crystal X-ray diffraction and magnetic susceptibility. The Ni(III) ions of both 1 and 2 form a 1D zigzag alternating magnetic chain within a column through Ni?S, Ni?Ni, Ni?N, S?S, or π?π interactions. Magnetic susceptibility measurements in the temperature range 1.8-300 K show that 1 exhibits antiferromagnetic behavior, while 2 shows a spin gap transition around 170 K, and antiferromagnetic interaction in the high-temperature phase (HT) and spin gap in the low-temperature phase (LT). The phase transition for 2 is second-order by determination of DSC analyses.     

Three ion-pair complexes containing bis(maleonitriledithiolate)copper(II) anion and substituted 4-dimethylaminopyridinium: Syntheses, crystal structures, and magnetic properties

Three new ion-pair complexes, [4RBzDMAP]₂[Cu(mnt)₂] (mnt²⁻ = maleonitriledithiolate; [4RBzDMAP]⁺ = 1-(4′-R-benzyl)-4-dimethylaminopyridinium, R = F(1), Cl(2) and Br(3)) were synthesized and characterized by elemental analyses, IR, UV, single crystal X-ray diffraction and magnetic measurements. The [Cu(mnt)₂]²⁻ anions and the cations stack alternately and form a 1D column via C-H···S, C-H···π or C-H···Cu interactions for 1 and 2. While the cations stack into a column though π···π or C-H···π interactions between pyridine and phenyl rings for 1 and 3. The change of the molecular topology of the counteraction when the 4-substituted group in the benzyl ring have been changed from F or Cl to Br atom, results in the difference in the crystal system, space group and the stacking mode of the cations and anions of 1, 2 and 3. Some weak hydrogen bonds between the adjacent columns further generate a 3D network structure. It is interesting that 1 and 2 exhibits antiferromagnetic coupling with θ = −2.372 K and θ = −14.732 K, while 3 shows weak ferromagnetic coupling feature with θ = 0.381 K.     

Ni(II) coordination compounds based on mixed phthalate and aromatic amine ligands: synthesis, crystal structures and magnetic properties

Three new coordination compounds, [Ni(Pht)(Py)₂(H₂O)₃] (1), [Ni(Pht)(β- Pic)₂(H₂O)₃] · H₂O (2) and [Ni(Pht)(1-MeIm)₂(H₂O)₃] (3) (where Pht²⁻ = dianion of o-phthalic acid; Py = pyridine, β-Pic = 3-methylpyridine, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy and thermogravimetric analysis. Crystallographic studies 1-3 reveal that each Ni(II) center has a distorted octahedral geometry being coordinated by two nitrogen atoms of aromatic amines, one oxygen atom from a carboxylate group of a phthalate ligand and three water molecules. Pht²⁻ anions act as monodentate ligands, while the remaining uncoordinated carboxylate oxygen atoms participate in the formation of hydrogen bonding. The uncoordinated oxygen atoms form hydrogen bonds with the coordinated water molecules from adjacent complexes creating a centrosymmetric dimer unit. Further, these dimer units are connected by O-H?O hydrogen bonds in double-chains. Depending on the nature of aromatic amines, the arrangement of these double-chains differs. The double-chains are held together only by van der Waals interactions in 1. In contrast, in 2 these chains form layers by π-π interactions between antiparallel molecules of β-Pic as well as by π-π interactions between β-Pic and Pht aromatic rings. In complex 3, the double-chains are knitted together via C-H?O hydrogen bonds between the methyl group of 1-MeIm and the coordinated carboxylate oxygen atom of Pht, as well as π-π contacts involving antiparallel 1-MeIm cycles. The thermal dependence of the magnetic susceptibilities for compounds 1 and 2 shows a weak antiferromagnetic interaction between the two Ni²⁺ ions of the hydrogen bonded dimers. For compound 3, a ferromagnetic interaction could be observed. Modeling the experimental data with MAGPACK resulted in: g = 2.22, |D| = 4.11 cm⁻¹ and J = −0.29 cm⁻¹ for compound 1, g = 2.215, |D| = 3.85 cm⁻¹ and J = −0.1 cm⁻¹ for compound 2 and g = 2.23, |D| = 4.6 cm⁻¹ and J = 0.22 cm⁻¹ for compound 3.     

Experimental and theoretical investigations of magnetic properties for two low-dimensional spin systems based on bis(2-thioxo-1,3-dithiole-4,5-dithiolato)nickelate monoanion building blocks

Two complexes of [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithiole-4,5-dithiolate) with nonmagnetic Schiff base cations, 1-(4-bromobenzylideneamino)pyridinium (4-BrBz-1-APy⁺; 1) and 1-(3-nitrobenzylideneamino)pyridinium (3-NO₂Bz-1-APy⁺; 2), have been characterized structurally. Their striking structural feature is the deviation of the [Ni(dmit)₂]⁻ anion from the square-planar environment around the Ni atom with 11.42° and 6.57° dihedral angles (between the mean molecular planes of two dmit²⁻ ligands) in 1 and 2, respectively. These twists arise from the molecular packing interactions between the superimposed anion and cation. In 1, the magnetic [Ni(dmit)₂]⁻ anions are arranged into a wave-shaped regular spin chain, whose magnetism was well fitted by one-dimensional (1D) Heisenberg uniform linear antiferromagnetic chain with |J/k_B| = 66 K. In 2, 1D ladder-shape [Ni(dmit)₂]⁻ chains are formed through lateral-to-lateral S?S contacts between the adjacent anions, which are further aligned into a two-dimensional (2D) anion layer via van der Waals forces. Complex 2 shows Curie-Weiss-type paramagnetic behavior with Curie constant C = 0.421 emu K mol⁻¹ and Weiss constant θ = −1.279 K. The broken-symmetry DFT approach was utilized to evaluate the magnetic coupling nature for 1 and 2, the theoretical analyses performed at ubpw91/lanl2dz level and concerned the so-called “weak bonding” regime approaches qualitatively explained the magnetic behaviors of 1 and 2.     

Syntheses, structures and magnetic properties of three new ion-pair complexes containing transition metal bis(malconitriledithiolate) anion and radical cations

Three new ion-pair complexes (m-MPYNN)₂Ni(mnt)₂ (1), (p-MPYNN)₂Ni(mnt)₂ (2) and (p-MPYNN)₂Cu(mnt)₂ (3) (m- or p-MPYNNI = [3- or4- (4,4,5,5-tetramethyl-1-oxido-3-oxyl-4,5-dihydro-3H-imidazol-2′-yl)-1-methylpyridinium] iodide, mnt = maleonitriledithiolate) have been prepared and characterized by elemental analyses, IR, single crystal X-ray diffraction and magnetic susceptibility. In complex 1, the m-MPYNN cations form a centrosymmetric dimer, and the [Ni(mnt)₂]²⁻ anion lies on a center of inversion. Complexes 2 and 3 show layered packing, and the p-MPYNN cations lie between the layers of the anions. Magnetic susceptibility measurements in the temperature range 2-300 K show that the three complexes exhibit weak antiferromagnetic behaviors. The behavior of complex 1 was explained with the singlet-triplet model.     

Synthesis, structure, sorption and magnetic properties of Ni(II) and Cu(II) complexes with thiosemicarbazone of 2-hydroxybenzaldehyde, bridged by 4,4′-bipyridine

(ML)₂(bipy) complexes (LH₂ = thiosemicarbazone of 2-hydroxybenzaldehyde, bipy = 4,4′-bipyridine, M = Ni(II), 1, or Cu(II), 2) were synthesized and characterized by X-ray crystallography. Compound 1 possessed porous structure due to peculiarities of crystal packing, whereas 2 formed infinite zig-zag chains with dense non-porous packing. It was shown that 1 absorbed 0.013 cm³/g of methanol vapor in two steps. Complex 1 was diamagnetic; for 2, the dependency of χ versus T could be interpreted by Bleaney-Bowers expression in 20-300 K temperature range (J = −6.8 cm⁻¹, g = 2.07).     

Interaction of Pt(II) and Pd(II) complexes of terpyridine with 1-methylazoles: A combined experimental and density functional study

The synthesis and characterization of several complexes of the composition [{M(terpy)}_n(L)](ClO₄)_m (M = Pt, Pd; L = 1-methylimidazole, 1-methyltetrazole, 1-methyltetrazolate; terpy = 2,2′:6′,2″-terpyridine; n = 1, 2; m = 1, 2, 3) is reported and their applicability in terms of a metal-mediated base pair investigated. Reaction of [M(terpy)(H₂O)]²⁺ with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO₄)₂ (1: M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H₂O)]²⁺ with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO₄ (3) in which the aromatic tetrazole proton has been substituted by the platinum moiety. For both platinum(II) and palladium(II), doubly metalated complexes [{M(terpy)}₂(1-methyltetrazolate)](ClO₄)₃ (4: M = Pt; 5: M = Pd) can also be obtained depending on the reaction conditions. In the latter two compounds, the [M(terpy)]²⁺ moieties are coordinated via C5 and N4. X-ray crystal structures of 1, 2, and 3 are reported. In addition, DFT calculations have been carried out to determine the energy difference between fully planar [Pd(mterpy)(L)]²⁺ complexes Ip-IVp (mterpy = 4′-methyl-2,2′:6′,2″-terpyridine; L = 1-methylimidazole-N3 (I), 1-methyl-1,2,4-triazole-N4 (II), 1-methyltetrazole-N3 (III), or 3-methylpyridine-N1 (IV)) and the respective geometry-optimized structures Io-IVo. Whereas this energy difference is larger than 70 kJ mol⁻¹ for compounds I, II, and IV, it amounts to only 0.8 kJ mol⁻¹ for the tetrazole-containing complex III, which is stabilized by two intramolecular C-H?N hydrogen bonds. Of all complexes under investigation, only the terpyridine-metal ion-tetrazole system with N3-coordinated tetrazole appears to be suited for an application in terms of a metal-mediated base pair in a metal-modified oligonucleotide.     

Mixed-ligand tris chelated complexes of Mo(IV) and W(IV): A comparative study

Two hitherto unknown mixed-ligand tris chelated complexes containing 2-aminothiophenolate, [Et₄N]₂[M^IV(NH-(C₆H₄)-S)(mnt)₂] (M = Mo, 1a; W, 2a) and two mixed-ligand tris chelate complex containing N,N-diethyldithiocarbamate, [Et₄N]₂[M^IV(Et₂NS₂)(mnt)₂] (M = Mo, 1b; W, 2b) have been synthesized and characterized structurally. Although these complexes are supposed to be quite similar to the well-known symmetric tris chelate complexes of maleonitriledithiolate (mnt), [Et₄N]₂[M^IV(mnt)₃] (M = Mo, 1c; W, 2c), but display both trigonal prismatic and distorted trigonal prismatic geometry in their crystal structure indicating the possibility of an equilibrium between these two structural possibilities in solution. Unlike extreme stability of 1b, 2b, 1c and 2c, both 1a and 2a are highly unstable in solution. In contrast to one reversible reduction in case of 1b and 2b, 1a and 2a exhibited no possible reduction up to −1.2 V and two sequential oxidation steps which have been further investigated with EPR study. Differences in stability and electrochemical behavior of 1a, 1b, 2a and 2b have been correlated with theoretical calculations at DFT level in comparison with long known 1c and 2c.     

Copper(II) complexes derived from tripodal tris[(2-ethyl-(1-pyrazolyl)]amine

Three mono-nuclear copper(II) complexes [Cu(tepza)X]ClO₄ (X = Cl, 1; X = NCS, 2; X = dca, 3) and two dinuclear bridging complexes [Cu₂(tepza)₂(μ-C₄O₄)](ClO₄)₂·H₂O(4) and [Cu₂(tepza)₂(μ-C₅O₅)](ClO₄)₂(5) where tepza = tris[2-ethyl(1-pyrazolyl)]amine, dca = dicyanamide, C₄O₄²⁻ = 3,4-dihydroxycyclobut-3-ene-1,2-dionate (squarate dianion) and C₅O₅²⁻ = 4,5-dihydroxycyclopent-4-ene-1,2,3-trionate (croconate dianion) were synthesized and structurally characterized by IR and UV-Vis spectroscopy as well as by single X-ray crystallography. In the solid state, the geometry of copper(II) centers in these complexes are as follows: close to SP in 2, distorted TBP in 3, predominant SP in 4, and distorted octahedral in 5, whereas in solution distorted SP geometry was generally found. The squarato and the croconato dianions in complexes 4 and 5 are bridging the two copper(II) centers in cis-bis-monodentate and bis-bidentate bonding modes, respectively. Magnetic susceptibility measurements at variable temperatures (2-300 K) reveal the weak antiferromagnetic coupling in the two bridging dinuclear complexes 4 (J = −24.9 cm⁻¹) and 5 (J = −3.1 cm⁻¹).     

Syntheses, crystal structures, and magnetic properties of two new 1D molecular solids based on Ni(mnt)2 ion

Two novel ion-pair complexes, 1-(4′-bromo-2′-fluorobenzyl)isoquinolinium-bis(maleonitrile dithiolato)nickel(III), [BrFBzIQl] · Ni(mnt)₂ · 0.5MeCN (1) and 1-(4′-bromo-2′-flourobenzyl)-quinolinium-bis(maleonitriledithiolato)nickel(III), [BrFBzQl] · Ni(mnt)₂ (2) have been characterized structurally and magnetically. The anions and cations of 1 stack into columns in the solid state, respectively; and the Ni(III) ions form uniform stacking column with the Ni?Ni distances 4.061 Å within a column through intermolecular Ni?S, S?S, Ni?Ni or π?π interactions, while 2 forms 1D column of alternating between cations and anions via the hydrogen bonds, C?N, C?N, N?C, and π?π interactions. The changes of coupling constants were observed in these two complexes at 85 K for 1 and 70 K for 2. It is interesting that 1 undergoes a transition from antiferromagnetic to ferromagnetic phase and 2 does counter to that of 1.     

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Pseudohalide-bridged five-coordinate Ni(II) or Co(II) complexes with bulky bidentate ligands: Magneto-structural correlationship

Bidentate ligands 2,2′-biquinoline (biq) and 6,6′-dimethyl-2,2′-bipyridine (dmbpy) with steric hindrance substituents cis to the nitrogen atoms have been used in the synthesis of transition metal complexes. Six new doubly end-on azido-bridged binuclear complexes [M₂(biq)₂(μ_1,1-N₃)₂(N₃)₂] (M = Ni (1), M = Co (2)), [M₂(biq)₂(μ_1,1-N₃)₂Cl₂] (M = Ni (3), M = Co (4)), [M₂(dmbpy)₂(μ_1,1-N₃)₂(N₃)₂] (M = Ni (5), M = Co (6)) and one end-to-end thiocyanato-bridged polymeric [Ni(dmbpy)(μ_1,3-SCN)(NCS)]_n (7) have been synthesized and characterized by single crystal X-ray diffraction analysis and magnetic studies. Complexes 1-6 comprise five-coordinate M(II) ions bridged by two end-on azide ligands. The bridging M-N-M bond angles are in the small range 104.1-105.2°. Complex 7 consists of a singly thiocyanate-bridged Ni(II) chain in which Ni(II) ions are five-coordinate. This research suggests that the bulky ligands play a key role in the formation of five-coordinate coordination structure. All complexes display intramolecular intermetallic ferromagnetic coupling with J_NiNi and J_CoCo of ca. 23 or 13 cm⁻¹ based on the Hamiltonian (S₁ = S₂ = 1 for Ni₂, or 3/2 for Co₂). The singly SCN⁻-bridged chainlike complex 7 shows intrachain ferromagnetic interaction with J = 3.96(2) cm⁻¹ and D = −4.55(8) cm⁻¹ (. Magneto-structural correlationship has been investigated.